Compass needle shows field around a high current wire on bench top.

Oersted's Expt.: Compass needle shows field around a high current wire. A large current (>100 amps) passes through a heavy, flexible copper cable, creating a circular magnetic field with the cable as its axis (determined by the right-hand rule). The compass needle tries to align itself so it is tangent to a circle drawn around the wire. Viewed from above, it appears that the needle swings so as to be perpendicular to the wire. The reversing switch can be thrown so that the current goes in the opposite direction, and the needle will swing in the opposite direction.